This invention relates generally to the production of kinescopes and particularly to an integrated thermal processing method for such production.
The production of color television picture tubes (kinescopes) is a very complex procedure employing literally hundreds of processing steps. Among the processing steps are those of producing a phosphor screen on the inside surface of a faceplate panel. The phosphor screen includes three different phosphors each of which produces one of the primary colors of light when impacted by electrons. The phosphor layer is coated with a layer of organic compound which provides a smooth surface so that a thin layer of aluminum can be applied to the screen. The aluminum coating is used to electrically connect the phosphor screen to the anode voltage supply and to a selection electrode (shadow mask) which causes each of three electron beams to impact the phosphor of the proper light emitting color. The aluminum layer also enhances the brightness of the image on the screen by reflecting toward the viewer light generated by the phosphor and which is directed toward the interior of the tube. After the aluminum layer is applied to the screen the panel assembly is heated to a temperature exceeding 300.degree. C. (cap bake) to remove the organic layer from the panel. The cap baking step is essential because organic substances remaining in the tube would adversely affect the subsequent processing of the tube. After the cap bake is completed, the shadow mask is inserted and the panel is ready to be joined to a funnel in preparation of being assembled into a finished kinescope.
The completed panel is permanently affixed to the open end of the funnel portion by applying a bead of low temperature melting glass frit material to the seal edge of either the panel or the funnel. The seal edges of the panel and funnel are mated and the assembly is raised to a temperature between 430.degree. and 450.degree. C. (frit seal temperature) to melt and crystalline the frit material and to permanently and hermetically seal the panel and funnel into an integral bulb.
An electron gun is mounted into the neck of the funnel portion and the bulb is heated to a temperature of about 300.degree. C. while being evacuated to the low internal pressure required for the proper operation of the kinescope. After the bulb is satisfactorily evacuated, the pumping port is hermetically sealed and the bulb continues on to other processing stages. Typically, the processing steps briefly described above are carried out while the various components move along conveyor lines and a large number of bulbs are continuously and simultaneously processed. Accordingly, each of the three heating operations, that is cap bake, frit seal and evacuation are effected in large ovens when a large number of bulbs are processed. Three individual heating steps are therefore employed during the production of each bulb. The use of separate heating stages is expensive, inefficient and time consuming. Also, because a large number of bulbs are continuously processed through the ovens, various processing techniques which can be effective in producing cleaner bulbs and in reducing thermal stresses in the bulbs cannot be utilized. A clean bulb contributes to increased bulb life and higher performance. Lowering thermal stresses reduces the probability of catastrophic implosion. For these reasons, there is a need for a method of producing kinescope bulbs which are scrupulously clean internally and which reduces thermal stresses, and which is substantially improved in efficiency and therefore is less expensive and less time consuming. The present invention fulfills these needs.